The acceleration of a bus is given by a(t) =α*t, where α = 1.2 m/s^3. If the bus's velocity at time t = 1.0s is 5.0 m/s, what is its velocity at time t = 2.0 s?
选项：

A:6.8 m/s;
B:5.6 m/s;
C:4.5 m/s;
D:7.6 m/s;
E:8.6 m/s;
F:5.1 m/s; G:5.3 m/s